1. Field of the Invention
The present invention relates mainly to a magnetic disk unit employed in office automation instruments.
2. Description of the Prior Art
In a conventional disk drive unit of the magnetic disk unit, as shown in FIG. 12, a rotor on which a magnetic disk is loaded is rotatably driven by a motor which is generally constructed of a spindle motor.
The spindle motor has a spindle mounted rotatably in a ball bearing unit to prevent the rotor's axial and radial vibrations. In the ball bearing unit, the spindle is mounted in a sleeve through a radial ball bearing constructed of an inner and an outer ring, and a plurality of balls disposed between these ring races.
In the conventional disk drive unit, the ball bearing unit and the rotor are separately constructed from each other, which increases the number of parts and the number of assembling works thereof.
Further, in such assembling works, it is necessary to mount the spindle on the rotor and to align the sleeve with a center of the ball bearing unit. Furthermore, such alignment work of the sleeve in center must be performed in a precise manner. Also required to prevent the axial and radial vibrations of the rotor are highly developed technologies. These requirements increase production costs of the magnetic disk unit.
In addition, in the conventional spindle motor of the disk drive unit, motor parts are separately constructed from the ball bearing unit.
Consequently, also in this respect, the number of parts and the number of assembling works are increased in the conventional disk drive unit. In addition, in assembling works of the disk drive unit, each of alignment works of the motor's parts with the ball bearing unit must be performed in a precise manner. These requirements increase manufacturing costs of the magnetic disk unit.